After arriving at Adirondack Park on our first family vacation since the start of the pandemic, I went out for my routine morning jog. The sun poured light over my body as if it was a racehorse in need of washing. And out there I saw unexpectedly a beautiful young deer near a lake. He focused his eyes on me to verify that I pose no danger. If I had fetched my cell phone to snap a photo, he would have disappeared. I chose to enjoy the view, savoring the moment as if the deer were a transient piece of music. In such instances, rare beauty cannot be documented or else it disappears. This left no way for me to share my rare experience with my family.

Past generations may have witnessed phenomena that were never documented in a scientific way. Is it possible that we missed important scientific clues from the past? Science relies on reproducibility of results, but we might need to wait a long time before rare events will repeat.

Let us consider a particular example. Suppose the solar system had been visited by technological equipment from an extraterrestrial civilization a few million years ago—hardly impossible since the age of the Milky Way galaxy is a million times longer than our recorded history. If we found a photo album with high-resolution images from that time, we would have an affirmative answer to Enrico Fermi’s paradox: “Where is everybody?” But the absence of that evidence doesn’t mean the answer is negative. If a tree falls in the forest and there is nobody around to hear it, does it make a sound?

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